Hello from Dorking!

Sadly I can’t help with your problem. When you have a turbo where a turbo should not be, mixed with an ECU which is a foreign introduction, any help from me would be a non starter & you’ve already got that problem.
You have done a majestic job so far, with every part illuminated, there is the hallmark of an artist, working to high engineering standards.
I’m sure you will provide us with “After” pictures but I would love to see your car in the metal.
Tremendous.
M

!st well done, the work looks great!
Check over all your electrical connections that have been disturbed during such extensive works, it would be understandably easy to have missed something.
ECUs just don't loose it from lack off use, I think the problem will be a simple one, in it's nature,  just maybe bloody difficult to track down.
Also check for dirty fuses and terminals, there may be a little corrosion built up over the extended period through exposure and lack of use.  
I'm sure the cure once found will be simple.
 

IT LIVES!!!  

Turns out stuck injectors were the culprit   Since this model and spec is unobtanium I bought a reconditioned and tested set.. also did a basic check on them when received, confirming they clicked when pulsed with 12v, but... 4 weeks later they managed to get stuck through lack of use   what gave me the initial hint was that just the plug on cylinder 1 had soot on it while the remaining 3 were bone dry. Took the injector rail out of the inlet, put some zip lock bags on each injector head and after cranking only the bag on the first cylinder had any fuel in it, even though it was the one furthest from the fuel line. They are also driven in pairs by the ECU,  so if it was an ECU problem, at least two of them should have fired.. many a love tap later and a jerry rigged testing/flushing jig and I managed to put together a set of 4 roughly working ones,  between the new and old ones! After that, it started almost the first time and once it warmed up a bit it started settling at around 1.1K revs, which is amazing!!